Some observations regarding steady laminar flows past bluff bodies

Fornberg, Bengt; Elcrat, Alan R.

doi:10.1098/rsta.2013.0353

Cited by 9 publications

(4 citation statements)

References 42 publications

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“…Our data on vortex parameters indicate that the vortices generated continuously downstream from backward-facing steps in the preserved paddlefish and the 3D models have the characteristics of forced (rotational) vortices rather than free (irrotational, potential) vortices [ 49 ]. Forced vortices are common at low to moderate Re (e.g., cavity flow and Moffatt eddies [ 50 – 52 ]; stable attached eddies generated by bluff bodies [ 53 ]). In a forced vortex, a continuous external source of kinetic energy must maintain the speed of the fluid throughout the vortex [ 54 ].…”

Section: Discussionmentioning

confidence: 99%

Physical modeling of vortical cross-step flow in the American paddlefish, Polyodon spathula

et al. 2018

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Vortical cross-step filtration in suspension-feeding fish has been reported recently as a novel mechanism, distinct from other biological and industrial filtration processes. Although crossflow passing over backward-facing steps generates vortices that can suspend, concentrate, and transport particles, the morphological factors affecting this vortical flow have not been identified previously. In our 3D-printed models of the oral cavity for ram suspension-feeding fish, the angle of the backward-facing step with respect to the model’s dorsal midline affected vortex parameters significantly, including rotational, tangential, and axial speed. These vortices were comparable to those quantified downstream of the backward-facing steps that were formed by the branchial arches of preserved American paddlefish in a recirculating flow tank. Our data indicate that vortices in cross-step filtration have the characteristics of forced vortices, as the flow of water inside the oral cavity provides the external torque required to sustain forced vortices. Additionally, we quantified a new variable for ram suspension feeding termed the fluid exit ratio. This is defined as the ratio of the total open pore area for water leaving the oral cavity via spaces between branchial arches that are not blocked by gill rakers, divided by the total area for water entering through the gape during ram suspension feeding. Our experiments demonstrated that the fluid exit ratio in preserved paddlefish was a significant predictor of the flow speeds that were quantified anterior of the rostrum, at the gape, directly dorsal of the first ceratobranchial, and in the forced vortex generated by the first ceratobranchial. Physical modeling of vortical cross-step filtration offers future opportunities to explore the complex interactions between structural features of the oral cavity, vortex parameters, motile particle behavior, and particle morphology that determine the suspension, concentration, and transport of particles within the oral cavity of ram suspension-feeding fish.

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Section: Discussionmentioning

confidence: 99%

Physical modeling of vortical cross-step flow in the American paddlefish, Polyodon spathula

et al. 2018

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“…• Step 6: Finally, in preparation for Step 2 of the subsequent time step, the complete forcings R V and R θ are evaluated and stored, subsuming all their respective counterparts detailed in (13). As all dynamics forcings are already available at the end of Step 5, the computational effort of this step is focused on evaluating the viscous terms.…”

Section: Solution Proceduresmentioning

confidence: 99%

“…However, benefits of the flexible meshing are not limited to global flows, and they can be equally important at finer-scale problems of computational meteorology; for example, in research and forecasting of weather in mountainous areas or over island archipelagoes. In their very essence, such problems can be thought of as flows past blunt bodies, among which a flow past a sphere historically plays a special rolecomplementary to a flow past a cylinder-and comprises a large portfolio of works employing theoretical, experimental and numerical methods [1,5,16,13].…”

Section: Introductionmentioning

confidence: 99%

Non-oscillatory forward-in-time integrators for viscous incompressible flows past a sphere

Szmelter

Smolarkiewicz

Zhang

et al. 2019

Journal of Computational Physics

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A non-oscillatory forward-in-time (NFT) integrator is developed to provide solutions of the Navier-Stokes equations for incompressible flows. Simulations of flows past a sphere are chosen as a benchmark representative of a class of engineering flows past obstacles. The methodology is further extended to moderate Reynolds number, stably stratified flows under gravity, for Froude numbers that typify the characteristic regimes of natural flows past distinct isolated features of topography in weather and climate models. The key elements of the proposed method consist of the Multidimensional Positive Definite Advection Transport Algorithm (MPDATA) and a robust non-symmetric Krylov-subspace elliptic solver. The solutions employ a finite volume spatial discretisation on unstructured and hybrid meshes and benefit from a collocated arrangement of all flow variables while being inherently stable. The development includes the implementation of viscous terms with the detachededdy simulation (DES) approach employed for turbulent flows. Results demonstrate that the proposed methodology enables direct comparisons of the numerical solutions with corresponding laboratory studies of viscous and stratified flows while illustrating accuracy, robustness and flexibility of the NFT schemes. The presented simulations also offer a better insight into stably stratified flows past a sphere.

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“…In the limit of vanishing viscosity, the Navier-Stokes equations lead to a fundamentally different set of solutions than the zero viscosity case, known as the Euler solutions which generally contain discontinuities. The infinite domain cases of 2-D flows past a cylinder and 3-D flows past a sphere are discussed in [6].…”

Section: Introductionmentioning

confidence: 99%

Solving 3D Magnetohydrostatics with RBF-FD: Applications to the Solar Corona

Mathews,

Flyer,

Gibson

2021

Preprint

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We present a novel magnetohydrostatic numerical model that solves directly for the forcebalanced magnetic field in the solar corona. This model is constructed with Radial Basis Function Finite Differences (RBF-FD), specifically 3D polyharmonic splines plus polynomials, as the core discretization. This set of PDEs is particularly difficult to solve since in the limit of the forcing going to zero it becomes ill-posed with a multitude of solutions. For the forcing equal to zero there are no numerically tractable solutions. For finite forcing, the ability to converge onto a physically viable solution is delicate as will be demonstrated. The static force-balance equations are of a hyperbolic nature, in that information of the magnetic field travels along characteristic surfaces, yet they require an elliptic type solver approach for a sparse overdetermined ill-conditioned system. As an example, we reconstruct a highly nonlinear analytic model designed to represent long-lived magnetic structures observed in the solar corona.

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Some observations regarding steady laminar flows past bluff bodies

Cited by 9 publications

References 42 publications

Physical modeling of vortical cross-step flow in the American paddlefish, Polyodon spathula

Physical modeling of vortical cross-step flow in the American paddlefish, Polyodon spathula

Non-oscillatory forward-in-time integrators for viscous incompressible flows past a sphere

Solving 3D Magnetohydrostatics with RBF-FD: Applications to the Solar Corona

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